1. Field of the Invention
The present invention relates to measurement of fluid pressure in fluid-containing, resilient tubing. In particular, the invention relates to a simple, non-invasive means for fluid pressure measurement in fluid-containing, resilient tubing by measuring the force exerted by the fluid-containing, resilient tubing when the tubing is mechanically compressed. The invention is particularly useful for field measurement of fluid pressure in drip irrigation systems.
2. Description of the Art
Microirrigation is increasing worldwide as a means of improving irrigation efficiency. Micro or drip irrigation systems can be adapted to hilly terrain and a wide variety of soils and crops. The emitting hose can be buried or laid on the soil surface. Most field crop drip systems use thin walled (4-15 mil), collapsible polyethylene tubing or drip xe2x80x9ctapexe2x80x9d with integral emitters. Tubing is manufactured in several diameters, with 16 mm (⅝ inch) diameter being the most popular (Hanson, et al., xe2x80x9cDrip irrigation of row crops: What is the state of the art?xe2x80x9d IN: National Irrigation Symposiumxe2x80x94Proceedings of the 4th Decennial Symposium, Nov. 14-16, 2000, Phoenix, Ariz.). Emitters are usually tortuous-path and uniformly spaced such that the tubing emits a xe2x80x9cnominalxe2x80x9d discharge per unit length of tubing when the pressure is maintained within desired limits. Typical drip tube pressures range from 34-138 kPa (5-20 psi), and pressures of 55-83 kPa (8-12 psi) are commonly used. The length of lateral is limited by the pressure loss and elevation variation. Pressure levels and variations in drip systems must be known to assess water distribution uniformity. Allowable pressure variations depend on the design uniformity (ASAE Standard EP 405.1, xe2x80x9cDesign and Installation of Microirrigation Systemsxe2x80x9d ASAE Standards 2000, American Society of Agricultural Engineers, St. Joseph, Mich.), but typically the pressure in a lateral should not vary by more than 20 percent. Unlike sprinkler nozzles, drip emitter pressure cannot be easily measured with a pitot-tube type insertion gage. Irrigators sometimes assess pressure by squeezing the tubing with their fingers. There is a need for a convenient, low-cost means to measure the pressure in drip tubing in the field, without disturbing or puncturing the tube.
The present invention is directed to a means for measuring pressure of fluid in fluid-containing, resilient tubing by measuring the force to mechanically compress the tubing to a predetermined distance.
More particularly, the means for measuring pressure of fluid in fluid-containing, resilient tubing comprises:
(a) first and second opposed members for receiving fluid-containing, resilient tubing therebetween;
(b) means for moving at least one of the members towards the other to a predetermined distance therebetween, to compress the fluid-containing, resilient tubing; and
(c) means connected to at least one of the members to measure the force exerted by the fluid-containing, resilient tubing against the members when the members are at the predetermined distance from one another; wherein the measuring means has been pre-calibrated at the predetermined distance, to correspond to fluid pressure within the fluid-containing, resilient tubing.
The invention provides a simple, non-invasive means for measuring fluid pressure in fluid-containing, resilient tubing. As shown in an exemplified embodiment, the invention senses pressure by compressing a section of fluid-containing, resilient tubing between two plates to a standard, repeatable percentage of its original diameter. The device can use any means to measure the force on the plates, such an electronic load cell or a simple compression spring. The measurement of the force on the plates corresponds to pressure units of fluid pressure exerted on the plates as pre-determined by a calibration equation or calibrated scale.
The invention is also directed to methods of using the apparatus of the invention.
The method of the invention for measuring pressure in fluid-containing, resilient tubing, comprises:
(a) compressing a section of fluid-containing resilient tubing between first and second opposed members to a predetermined distance, and
(b) measuring the force exerted by the fluid-containing, resilient tubing against the members when the members are at the predetermined distance from one another; wherein the measuring means has been pre-calibrated, at the predetermined distance, to correspond to fluid pressure within the tubing.
An important application of the invention is for field measurement of fluid pressure in drip irrigation systems. Drip irrigation using thin-walled plastic drip tape with integral emitters is increasing worldwide as a means of improving irrigation water use efficiency. Irrigation uniformity depends on maintaining pressure in drip laterals within acceptable limits. Typical drip tube pressures range from 34-138 kPa (5-20 psi), and a common tube diameter is 16 mm. To date, there has been no easy method of measuring the internal pressure in drip tubing in the field without puncturing the tube or installing special fittings. The invention provides a low-cost means for fluid measurement in drip irrigation systems and is suitable for field use. As demonstrated in the Example, below, it can measure pressure within about 5 percent accuracy.
Accordingly, it is an object of the invention to provide a convenient, non-intrusive and low cost means for irrigators to assess pressure variations within irrigation systems, e.g., microirrigation laterals, without installing special fittings or puncturing the tubing.
Most drip tubing in the field is buried from 2 to 40 cm. Shallow buried tubing is easily exposed for testing. Even when placed under plastic mulch, the tubing is often exposed at the upstream and downstream ends. Deeply buried tubing would need to be exposed by digging a hole. In either case, this non-intrusive pressure measurement is preferable to punching and repairing a hole in the tubing for direct pressure measurement.
Other objects and advantages of the invention will become readily apparent from the ensuing description.